By Sara Sjolin, MarketWatch

LONDON (MarketWatch) -- Supermarket chain Tesco tumbled on Friday after issuing a profit warning, capping gains for the FTSE 100, which posted its first monthly gain since May.

Tesco shares (TSCDY) slumped 6.6% after the company warned on profit for the third time in three years, saying it will slash its interim dividend and reduce capital expenditure as it battles with fierce competition.

The company -- which is the U.K.'s largest retailer -- now expects full-year trading profit in the range of 2.4 billion pounds ($3.98 billion) to GBP2.5 billion.

"We have now lost count of the number of times that we have downgraded our forecasts for Tesco over the last three years or so," analysts at Shore Capital said in a note.

Other supermarket chains were hit by the downbeat Tesco news, with shares of J Sainsbury PLC 4.4% lower, Wm Morrison Supermarkets PLC off 5% and Marks & Spencer Group PLC down 1.9%.

More broadly in London, the FTSE 100 index rose 0.2% to close at 6,819.75, partly recovering from a 0.4% decline on Thursday that was spurred by renewed tensions in Ukraine. For August, the index posted a 1.3% gain, its first monthly advance since May.

Among stocks climbing on Friday, miners staged a rebound after sharp losses on Thursday. Shares of Anglo American PLC gained 1.2% and BHP Billiton PLC (BHP) picked up 0.9%.

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